The gaseous phytohormone, ethylene, has profound effects on plant grown and development. A transcriptional cascade that is initiated by a transcription factor, EIN3, has been uncovered in the ethylene signal transduction pathway. However, little is known about how EIN3 responds to the incoming ethylene signal. In additional, the biological roles of a group of newly identified EIN3 homologs, EILs, in ethylene responses have largely been unexplored. The goal of this proposed research is to explore the biochemical mechanism of EIN3 protein in response to ethylene signaling as well as to investigate the functions of EIL genes in ethylene-regulated processes. The protein stability, phosphorylation modification, and subcellular localization of EIN3 protein will be assessed in the presence or absence of ethylene. In addition, other molecules that modulate the function of EIN3 will be identified by either protein-protein interaction assays or a genetic screen for ein3 suppressors. At last, loss-of-function mutations and transgenic overexpression plants of various EIL genes will be analyzed. A genome-wide gene expression profiling will also be conducted in ein3/eil mutants and overexpression plants to identify their respective targets. The elucidation of EIN3 action and the characterization of EIL functions will greatly improve our understanding of how ethylene gas exerts its effects on plant adaptation and fitness, and consequently enable us to favorably manipulate the ethylene responses in those agriculturally important crops.